"The longer this controversy persists the more precarious Baroness Scotland's position becomes. Her survival in office continues to hang by a thread and to divert attention from Labour's efforts at its party conference to move on."

But Brown said today he had looked at the matter "very carefully", describing it as a "serious issue".

"I have looked at this and Baroness Scotland acted in good faith at all times," he told BBC1's Andrew Marr Show.

"She did not hire someone she knew to be an illegal worker, she checked the documentation and so would dispute what the person is saying.

"But I think the most important thing is that the borders control agency looked at this issue."

He added: "Her mistake was not to keep copies and for that she was rightly fined and has profusely apologised."

Scotland restated her position in a statement last night, saying: "For the record, as I have said previously, I was shown all relevant documents – a P45, national insurance details, a marriage certificate, a letter from the Home Office, references, and a passport – by Ms Tapui during her job interviews. I have nothing further to add."

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